Maximum Radar Cross Section Reduction Research Articles

Terahertz RCS reduction employing reconfigurable graphene-based AMC structures

Recently, modern technology has towards stealth technology, especially in military applications so, this paper presents a terahertz radar cross-section (RCS) reduction utilizing reconfigurable graphene-based artificial magnetic conductor (AMC) arrays. The AMC unit cell has a Vivaldi shape with circular slots etched in the radiator to reduce the RCS from metallic surfaces at THz bands. The AMC cells affect the surface impedance of the metallic objects which reduces the reflected EM waves from them. The RCS reduction bandwidth is achieved and controlled by varying the voltage applied to graphene cells which varies its chemical potential (µc). The effect of changing the graphene conductivity on the RCS reduction is investigated. Different arrangements to obtain maximum RCS reduction are presented. A 12 × 12 hybrid arrangement of the graphene-based AMC structures achieved maximum RCS reduction from 1.5 to 4 THz with 22 dB greater than the unloaded metallic surface. The CST simulator is employed in the simulation.

Multi-heterointerface integration in nitrogen-doped Ti3C2Tx@Fe3O4 nanocomposites for superior microwave absorption

Engineering a lightweight and thin microwave absorber through the design of multiple heterogeneous interfaces represents a significant challenge. Here, we synthesized a nitrogen (N)-doped Ti3C2Tx@Fe3O4 (N–Ti3C2Tx@Fe3O4) nanocomposite with a sandwich-like structure through a solvothermal approach using hydrazine hydrate as the N donor. The numerous Ti3C2Tx electron transfer pathways of Ti3C2Tx enable the realization of a hierarchical conduction network within N–Ti3C2Tx@Fe3O4. The introduction of defects through N doping and the integration of Fe3O4 with Ti3C2Tx are pivotal for enhancing the dipole polarization. The heterogeneous interfaces in N–Ti3C2Tx@Fe3O4, coupled with Fe3O4 components, substantially boost the electromagnetic wave (EMW) absorption performance of the composite. An optimal N integration and the loading of Fe3O4 in Ti3C2Tx result in an improved impedance matching of N–Ti3C2Tx@Fe3O4. The synergistic effect of the improved impedance matching and the strong EMW attenuation capability endow N–Ti3C2Tx@Fe3O4 with enhanced microwave absorption (MA) properties. Specifically, at a thickness of 1.04 mm, the composite exhibits the effective absorption bandwidth (3.92 GHz; 14.08–18.00 GHz), surpassing that of Ti3C2Tx. At a thickness of 0.98 mm, it exhibits a maximum reflection loss of −40.28 dB at 17.25 GHz, which substantially exceeds that of Ti3C2Tx. Furthermore, it shows a maximum Radar Cross Section reduction of 21.32 dB cm2. A cotton fabric was coated with N–Ti3C2Tx@Fe3O4, and it was found to exhibit enhanced heat conduction and dissipation, at rates 3.83 and 4.64 times greater than those of uncoated cotton, respectively. These results highlight the considerable potential of N–Ti3C2Tx@Fe3O4 nanocomposites for use in far-field applications. It is envisaged that the exceptional MA and thermal management properties of N–Ti3C2Tx@Fe3O4 nanocomposites will provide a novel avenue for crafting lightweight and thin EMW absorbing materials.

Novel digital terahertz device for three-state logic gate and phase coding based on graphene and Schottky barrier junctions

Terahertz technology, III-V group semiconductor devices, and graphene have great potential for broad applications in 6 G wireless communications. A novel digital terahertz device with nickel/GaN and graphene/GaN Schottky barrier junctions was proposed in this study. The patterned metal electrodes of the device, together with the graphene layer, formed a terahertz metasurface. The mechanisms of modulating the fermi level of graphene and the conductivity of the device to manipulate the transmission coefficient and reflected phase of terahertz waves were investigated using numerical calculations. The electrical and optical simulation results theoretically demonstrated that the three-state logic gate operation for the transmission coefficient of terahertz wave at 1.458 THz and the 1-bit reflected phase coding manipulation in 1.51–1.55 THz were realized. In addition, the maximum radar cross section reduction for the reflected wave was approximately 11.14 dB, comparing the designed coding sequences with the metal plate. These functions are mainly implemented by applying an external bias voltage to the device. This study provides a new and feasible strategy for designing digital terahertz manipulation devices.

A broadband AMC metasurface for radar cross section reduction and application in microstrip antenna

ABSTRACTA broadband checkerboard artificial magnetic conductor (AMC) metasurface with a 61% bandwidth is proposed. Two different AMC unit cells with 180° (±37°) effective reflection phase difference over a wide frequency range from 7.3–14 GHz are designed. A checkerboard metasurface is structured with two AMC unit cells and is applied in a microstip antenna for radar cross section (RCS) reduction. The simulated results show that the antenna can achieve more than 10 dB RCS reduction from 7.2–13.1 GHz. The maximum RCS reduction is 36 dB. Meanwhile, the radiation performance of the antenna has been well kept. Finally, the low RCS antenna is manufactured and measured. The measured results are in agreement with the simulations.

Surface morphology of magnetic carbon foam regulated electromagnetic properties for microwave absorption

Electromagnetic pollution resulting from the electronic communication can be mitigated by using microwave absorbers. The magnetic N-doped carbon foams with diverse surface morphologies as absorbers were synthesized via alkalization treatment, hydrothermal reaction, and carbothermic reduction reaction. The microstructure, electromagnetic parameters, and microwave absorption properties can be tailored by adjusting thermal treatment temperatures. The results indicated that the composites exhibit exceptional microwave absorption properties, with a minimum reflection loss of −44.15 dB at 11.18 GHz and an effective absorption bandwidth of 5.3 GHz at a thickness of 1.53 mm. The exceptional microwave absorption properties can be attributed to the synergistic effect of superior impedance matching, robust dielectric loss, and magnetic loss. The far-field radar cross section (RCS) is also reduced, achieving a maximum RCS reduction value of 14.6 dBm2. The present study presents a novel concept for the fabrication of lightweight and broadband microwave absorbing materials.

ZIF-67 derived Co@carbon nanotubes anchored on carbon fiber for efficient microwave absorption and mechanical enhancement

Rational design of multifunctional and high-performance electromagnetic wave (EMW) absorbers is highly desirable but still remains a challenge. Herein, the 3D heterostructural Co@carbon nanotubes/carbon fiber (Co@CNTs/CF) hybrids derived from ZIF-67/CF were successfully fabricated via the in-situ synthesis of ZIF-67 on CF and subsequent catalytic chemical vapour deposition. Intriguingly, the as-obtained composites acquire adjustable EMW absorption and favorable mechanical properties simultaneously. Specifically, taking advantage of adequate conductive paths, plentiful heterogeneous interfaces, suitable defect vacancies, appropriate magnetic loss, as well as optimized impedance matching, Co@CNTs/CF delivers a brilliant EMW absorption intensity of −45.11 dB at only 1.15 mm together with a broad effective absorption bandwidth (EAB) of 4.0 GHz (1.23 mm), and an unexpected minimal reflection loss up to −65.63 dB (3.84 GHz) coupled with an EAB of 3.6 GHz at merely 1.09 mm, respectively. In addition, the tunable EAB can be achieved in 2.6–18 GHz, covering 96 % of the test frequency by changing the absorber thickness from 0.93 to 5.0 mm (29 wt%). Moreover, the maximum radar cross section reduction can reach 48.8 dBm2. The uniform layer of CNTs with moderate crystallinity also enables Co@CNTs/CF to improve the tensile strength and Weibull modulus compared to unsized CF. This study paves a novel avenue for developing multifunctional materials based on CF through an efficient, controllable and low-cost approach.

All-Metal Coding Metasurfaces for Broadband Terahertz RCS Reduction and Infrared Invisibility

With the rapid advancement of modern technology and radar detection systems, electromagnetic (EM) stealth technology has become increasingly significant, particularly in aircraft stealth and military radar applications. In this work, an all-metal metasurface is designed for broadband terahertz radar cross-section (RCS) reduction and infrared invisibility. The all-metal metasurface possesses extremely low infrared emissivity and high polarization conversion in the terahertz band. Through the joint simulation of MATLAB and CST, a genetic algorithm is used to optimize the random phase distribution of 2, 3, and 4-bit metasurfaces, so that the reflected wave is scattered to achieve broadband terahertz RCS reduction. Simulation results show that the metasurface can simultaneously achieve broadband terahertz RCS reduction in 3–5 THz and infrared invisibility in 24–38 THz (8–12.5 μm). The RCS reduction of the coding metasurface is greater than 10 dB compared to the metal plate, and the maximum RCS reduction of the 4-bit metasurface can reach 21.1 dB. Compared to the traditional design method, the proposed method can reduce time consumption and find the optimal result to achieve high performance. We believe the proposed method can provide significant guidance for surface coating in camouflage applications and opens up new possibilities for improving the information capacity of coding metasurfaces.

A new stitched-plain weave fabric composite structure with reduced broadband radar cross-section

In this paper, a new stitch-plain weave fabric composite (SPWF) by acupuncture technology is proposed. Two patterns are designed, one is a typical chessboard layout (SPWF-1), and the other is a layout optimized by a genetic algorithm (SPWF-2). Simulated and experimental results show that SPWF can disperse electromagnetic wave energy in all directions and effectively reduce the radar cross-section (RCS) in the frequency range of 12.5 GHz−26.5 GHz, and the maximum RCS reduction for SPWF reaches −40 dB. The tensile modulus and strength of SPWF-1 are predicted by finite element method, and the results are in good agreement with the experimental data. In addition, a new optimization objective function is proposed to design the patterns of SPWF-2.

Reconfigurable chessboard coding plasma-based dielectric resonator structure for RCS reduction

In this paper, reconfigurable chessboard coding plasma-based dielectric resonator structure for radar cross section reduction is investigated. The radar cross section (RCS) reduction is essential in military applications. The metallic conductor surface is covered with plasma-based dielectric resonator (DRA) unit-cells arranged in chessboard configuration. The plasma DRA unit-cell consists of concentric cylindrical ring filled with ionized plasma placed over FR4 dielectric substrate. The plasma ionization voltage values are tuned to reflect the electromagnetic wave with phase shift of 180° and equal amplitudes. The phase 0° state represents the logic “0” while the phase 180° state represents the logic “1”. The chessboard arrangement consists of super-cells with 0/1 logic states. Different sizes of uniform super-cells 3 × 3, 4 × 4, 6 × 6, and 12 × 12 unit-cells are investigated for maximum RCS reduction. The scattered beams are directed to (± 30°, 180° ± 30°), (± 25°, 180° ± 25°), (± 20°, 180° ± 20°), (± 15°, 180° ± 15°) and (± 10°, 180° ± 10°) for 3 × 3, 4 × 4, 6 × 6, 8 × 8, and 12 × 12 uniform super-cells, respectively. The RCS is reduced over a wide angle range reduction with − 18 dBm2 at the broadside direction and below − 32 dBm2 over the angular range from − 90° to 90° according to the super-cell size. The non-uniform allocation of unit-cells in the super-cell chessboard arrangement is investigated. The RCS reduction bandwidth extended from 8.5 to 9.65 GHz. The scattered beam produces null in the broadside direction with wideband RCS reduction. The proposed structures are simulated using CST-MWS electromagnetic simulator.

Hybrid frequency selective surface phase cancelation structure based broadband switchable radar cross section reduction

In this paper, a switchable radar cross section (RCS) reduction between the two broadbands' (1-7 GHz and 4-10 GHz) has been achieved by just considering the integration of hybrid frequency selective surface (FSS) based phase cancelation structure (PCS) with a modified ground square patch antenna operating at 2.4 GHz. The full metallic ground plane of the conventional microstrip antenna (MSA) is replaced by a 2 × 2 array of band-stop FSS having the same frequency as that of the MSA. This ground plane modification helps to increase the maximum out-of-band RCS reduction from 16.4 dB to 20 dB. The ground modified MSA without any PCS exhibits both in-band and out-of-band maximum RCS reduction of 20 dB over a wideband (1-7 GHz). A new approach is adopted to form the PCS. It is formed by placing two non-overlapping hybrid FSSs at different heights above the MSA. The MSA with FSS based ground plane along with the hybrid FSS based PCS exhibits good monostatic and bistatic RCS reduction across 4 to 10 GHz without affecting the radiation characteristics of the conventional MSA. The measured results show a close resemblance to the simulated ones.

X-band RCS Reduction of Airborne Antenna Array Using Loaded PIN Diodes

The paper applies PIN diodes to airborne microstrip antenna array to achieve radar cross section (RCS) reduction while the array is not at work, thus enhance the stealth performance of the aircraft. PIN diode can be regarded as a variable resistance or capacitance when it is forward-biased or reverse-biased, respectively. The equivalent resistance value of PIN diode in the forward-biased state is optimized and the radiation performance of the antenna array is not seriously affected. Simulation results show that the method can dramatically reduce the antenna RCS by disturbing the electric field distribution of current incident wave. The experiment results depict that maximum RCS reduction of aircraft model is more than 25dB, thus validates the proposed method.

Wideband, Very Low RCS Engineered Surface With a Wide Incident Angle Stability

In this communication, broadband, low radar cross section (RCS) engineered surface with the ability of operating over a wide range of oblique incident angles is presented. Two types of artificial magnetic conductor (AMC) unit-cells with a 180° ± 37° reflection phase differences are developed. Perforated superstrate is loaded on the top of conventional metallic patch-based AMC unit-cells which contributes to oblique incidence stability up to 60°. Moreover, it results in a wide operational frequency range of 16.5–58 GHz under normal incidence. To satisfy the periodicity condition, an appropriate number of proposed AMC unit-cells are considered as a super-cell. Then for the first time, the type and size of super-cells are optimized simultaneously. In consequence, maximum RCS reduction with a very uniformed scattered pattern is achieved. The superiority of the new arrangement over conventional coding arrangements is investigated for both monostatic and bistatic RCS results. It is shown that new structure results in a wider bandwidth, greater RCS reduction level and more uniformed scattered patterns. The proposed surface exhibits a very broadband of 111.5% for −10 dB normalized RCS reduction under normal incidence. A prototype is fabricated, and the experimental results showed promising agreement with the simulated ones.

A Polarization Conversion Coding Metasurface for Broadband Radar Cross-Section Reduction

We have designed a polarization conversion coding metasurface (CM) for broadband radar cross-section reduction. The CM is made up of a kind of deformed bowtie-shaped particle and its mirror, named “0” and “1”, respectively, which can realize cross-polarization conversion under the vertical incidence of a linearly polarized wave. According to the coding sequence optimized by the genetic algorithm, the two kinds of unit are arranged to form a design, called a 1-bit CM, which can scatter electromagnetic waves in various directions. The simulation results demonstrate that the two kinds of unit can achieve more than a 90% polarization conversion ratio, and the whole CM can realize more than a 10-dB reduction of monostatic radar cross-section (RCS) from 8.8 GHz to 20.9 GHz, while the maximum RCS reduction of 32.5 dB can be obtained at 14 GHz under the normal incidence of x- and y-polarized waves. The experimental results are almost identical to the simulation. Thus, we believe that the designed 1-bit CM can be well applied for the stealth business.

Epsilon near zero metasurface for ultrawideband antenna gain enhancement and radar cross section reduction

A non-resonant metamaterial unit cell is proposed to design a metasurface for ultrawideband (UWB) gain enhancement and radar cross section (RCS) reduction of an UWB antenna. Epsilon near zero (ENZ) property and negative refractive index of metamaterial is achieved to ensure low loss and amplification of electromagnetic waves (EM) passing through it. The proposed metamaterial is designed on a 6 mm × 6 mm FR4 substrate with dielectric constant 4.4, height 1.6 mm and loss tangent 0.01. The unit cell is simulated with periodic boundary condition to get the properties of periodically arranged unit cells in one plane called metasurface. A Metasurface is designed by planar arrangement of 5×5 unit cells of proposed metamaterial unit cell and is kept at height of 2 mm above an ultrawideband planar microstrip antenna. Antenna system with metasurface has physical and electrical dimensions of 32 × 32 × 5.2 mm3 and 0.34λ0×0.34λ0×0.05λ0 respectively, where λ0 is the free-space wavelength at 3.2 GHz. The bandwidth of UWB patch antenna (3.1–10.6 GHz) is unaffected by the presence of metasurface. The analysis of radiation mechanism shows the phase difference of EM waves passing through metasurface with and without reflection is 300°–400°. This indicates emergence of coherent waves from metasurface and contributes in gain enhancement. Maximum gain is 5.7 dB at 6.8 GHz with radiation efficiency of 88.5% and maximum gain enhancement is 10.1 dB at 9.8 GHz. The reflection phase analysis of normal incident wave predicts the frequency for maximum RCS reduction as 6.4 GHz. Maximum RCS reduction of antenna with application of metasurface is 21 dB at 6.7 GHz. Significant gain enhancement and reduction of RCS is achieved for ultrawideband. The proposed antenna system metasurface with enhanced gain and reduced RCS is a good candidate for application in stealth and military platforms.

Design of Low RCS Circularly Polarized Patch Antenna Array Using Metasurface for CNSS Adaptive Antenna Applications.

A low radar cross section (RCS) circularly polarized patch antenna array operating at the downlink S-band (2492 ± 5 MHz) of the Chinese Compass Navigation Satellite System (CNSS) is proposed. The low RCS is achieved by replacing the conventional metallic ground with an artificial magnetic conductor (AMC)-based metasurface. Two different AMC unit cells are designed having a phase difference within 180 ± 37° and combined in a chessboard-like configuration to realize the AMC-based metasurface. Furthermore, the AMC-based metasurface is utilized as the ground of the CNSS array for wideband RCS reduction. A wideband RCS reduction from 6 GHz to 17 GHz is achieved due to the wideband diffusion property of the AMC unit cells. The maximum RCS reduction is more than 14 dB at 13.3 GHz irrespective of the polarization direction of the incident waves. Moreover, the circular polarization (CP) performance is realized by embedding a circular slot on the patch radiator of the antenna element. The radiation characteristics of the CNSS array are hardly impacted by the inclusion of the metasurface-based ground. The proposed CNSS array has been fabricated and measured. The measurement results are in reasonable agreement with the simulations. The proposed CNSS array can be a good candidate for CNSS adaptive antenna applications where low RCS is simultaneously demanded.

Compact low radar cross‐section microstrip patch antenna using particle swarm optimization

AbstractA new approach for in‐band radar cross section (RCS) reduction of microstrip patch antenna with preserved radiation features is presented. This aim is achieved by the application of highly absorbing unit cells optimized by particle swarm optimization around the radiating patch of the reference antenna. More than 10 dB in‐band RCS reduction is observed from 2.5 GHz to 3 GHz for both x‐ and y‐polarizations with a −26.4 dB maximum RCS reduction at 2.8 GHz, according to measurement results. A close agreement between the measured and the simulated results shows that the proposed absorbing unit cell is a good candidate to enhance antenna in‐band stealth performance. In addition, with a comparative table, it has been shown that the proposed antenna has much lower in‐band RCS and is more compact than the other antennas proposed in previous literature. The basic benefit of this study is to achieve maximum in‐band RCS reduction, especially at the exact desired frequency without long‐term simulations and time‐consuming design studies.

Design of a wideband polarisation conversion metasurface and its application for RCS reduction and gain enhancement of a circularly polarised antenna

An improved loading method of checkerboard-based linear polarisation conversion metasurface (PCM) is proposed for gain enhancement and wideband radar cross-section (RCS) reduction of the circularly polarised patch antenna (CPA). The proposed metasurface consists of a checkerboard arrangement of PCM and its mirror unit cells, and an improved loading method is used to rearrange the PCM unit cells around the radiating patch. The PCM unit cell is composed of a metallic pattern on the top and bottom surface covered with metal. A wideband RCS reduction is realised by achieving 180° cross-polarisation reflection phase difference between the two neighbouring PCM unit cells and gain enhancement is achieved by the coherent superposition of energy in the far-field between the radiating patch and PCM cells. Simulated and measured results depict that the operating bandwidth of CPA and the proposed antenna is 12.6-13.76 GHz. The peak gain of the proposed antenna is 3.5 dB higher than the CPA and 3-dB axial ratio bandwidth of the designed antenna is 200 MHz. The proposed antenna achieves significant RCS reduction in the frequency range of 9.6-22.6 GHz with maximum in-band RCS reduction of 21 dB and maximum out of band RCS reduction of 34 dB.

Low RCS and High-Gain Patch Antenna Based on a Holographic Metasurface

In this letter, a low radar cross section (RCS) patch antenna based on a holographic metasurface (HM) is proposed. An HM is designed to form the proposed antenna. As a parasitic structure of the antenna, the proposed HM can effectively increase the antenna radiation aperture; thus, a relatively high gain is obtained. At the same time, the HM has the ability to transform a propagating wave into a surface wave. Therefore, the backscattering is greatly reduced, resulting in a low monostatic RCS. A high gain as much as 10 dBi and a wideband radar cross section reduction (RCSR) ranging from 5.5 to 21.5 GHz have been achieved. It is also worth pointing out that the maximum RCSR is 21.64 dB around 8 GHz for both x - and y -polarized incident waves. The proposed antenna has been fabricated and measured. Good agreements beween the simulated and measured results are observed.

Wideband radar cross section reduction of a microstrip antenna with square slots

AbstractThis paper proposes a new radar cross section (RCS) reduced microstrip antenna incorporating 475 square slots on the patch. The proposed antenna achieves wideband RCS reduction with radiation performance sustained. The modified and reference antenna are simulated and analyzed in radiating and scattering mode, respectively. Prototypes of two antennas are fabricated and measured. Compared with the reference antenna, the simulated result shows the modified antenna RCS reduced in the frequency range 1.1–2.6 GHz, which contains the in-band and out-of-band frequency band simultaneously. And the maximum RCS reduction is 7.6dB at the frequency of 1.19GHz. Besides, the modified antenna can achieve the antenna RCS reduction in the case of oblique incidence. The prototypes of two antennas are fabricated and measured, and the accuracy of the simulation is proved by the measured result. Due to its advantages of simplicity, wideband RCS reduced, broad-angle RCS reduced, the method in this paper is suitable for wideband antenna RCS reduction in space-limited environment.

Analysis and design of an ultra-thin metamaterial absorber and its application for in-band RCS reduction of antenna

ABSTRACTThis paper presents the analysis and design of an ultra-thin metamaterial absorber (MA) for the in-band Radar Cross Section (RCS) reduction of a patch antenna. The proposed MA consists of a periodic array of double square loop structures printed on an FR4 substrate with a thickness of 0.022 λo. A detailed theoretical analysis of the MA unit cell is conducted to investigate the absorbing characteristics of the MA. The simulated and measured results show that MA significantly reduces the RCS of the proposed antenna within its impedance bandwidth and a maximum RCS reduction of 15 dB is achieved at 6.75 GHz. The impedance bandwidth of the proposed antenna is 6.6–7 GHz, which is also improved by the loading of the MA. The results also show that after loading the MA on the patch antenna, the RCS of the proposed antenna is significantly reduced and there is no degradation observed in its radiation properties.